1. Field of the Invention
This invention relates to an agricultural and horticultural granular composition comprising a major proportion of particles having a size of from 105 .mu. (150 mesh) to 297 .mu. (48 mesh), "mesh" being according to the Tayer Standard Screen Sieves.
2. Description of the Prior Art
In recent years, the spraying of agricultural chemicals in the form of dusts or granules by means of helicopters or multi-nozzle hose dusters has been practiced in order to save labor in the spraying operation. Since the dusts or granules have various defects which make them unsuitable for spraying by such methods, particles having an intermediate size between a dust and a granule, i.e. a size of 105 .mu. (150 mesh) to 297 .mu. (48 mesh), have come forth as promising formulations of agricultural chemicals from the standpoint of effect and prevention of public hazards. Compositions having such a size distribution are prepared either by coating an agricultural chemical and a suitable assistant on to the surface of the carrier particles, which have been previously sifted to the desired size, or by absorbing them into a granular carrier. These formulating methods involve simple process steps, but still have many defects. According to these methods, carrier particles which have been sifted to the desired sizes of 48 to 150 mesh are used, and therefore, this imposes a limitation on the supply of carriers and constitutes a drawback against mass-production.
If a non-absorbing substance, such as calcium carbonate or silica is used as a carrier in the above-mentioned size range, the active ingredient does not penetrate into the carrier particles when applied by a coating method, and therefore, it is difficult to form a composition having an active ingredient concentration above certain level. In addition, as the coated portion has a high concentration of the active ingredient, it has the defect of causing phytotoxicity or posing toxicity problems for humans because the coated portion may be stripped off and become powdered by direct contact with the human body or during transportation or spraying.
On the other hand, absorbing granular carriers usually have a high surface activity, and may be easily decomposed, depending upon the properties of the active ingredient. Furthermore, since the active ingredient is strongly adhered to the inner part of such carrier particles, the release of the active ingredient is slow and incomplete, therefore the effect is not sufficient.